Reinhard Kleeberg

SOME SUCCESSFUL APPROACHES TO QUANTITATIVE MINERAL ANALYSIS AS REVEALED BY THE 3RD REYNOLDS CUP CONTEST

Details of the quantitative techniques successfully applied to artificial rock mixtures distributed for the third Clay Minerals Society Reynolds Cup (RC) contest are presented. Participants each received three samples, two containing 17 minerals each and a third containing ten minerals. The true composition of the samples was unknown to all participants during the contest period. The results submitted were ranked by summing the deviations from the actual compositions (bias). The top three finishers used mainly X-ray diffraction (XRD) for identification and quantification. The winner obtained an average bias of 11.3% per sample by using an internal standard and modified single-line reference intensity ratio (RIR) method based on pure mineral standards. Full-pattern fitting by genetic algorithm was used to measure the integrated intensity of the diagnostic single-line reflections chosen for quantification. Elemental-composition optimization was used separately to constrain phase concentrations that were uncertain because the reference mineral standards were lacking or not ideal. Cation exchange capacity, oriented-sample XRD analysis, and thermogravimetric analysis were also used as supplementary techniques. The second-place finisher obtained an average bias of 13.9%, also by using an RIR method, but without an added internal standard and with intensity measured by whole-pattern fitting. The third-place finisher, who obtained an average bias of 15.3%, used the Rietveld method for quantification and identification of minor phases (using difference plots). This participant also used scanning electron microscopy (with X-ray microanalysis) to identify minor components and verify the composition of structures used in Rietveld analysis. As in the previous contests, successful quantification appears to be more dependent on analyst experience than on the analytical technique or software used.

QUANTITATIVE PHASE ANALYSIS OF BENTONITES BY THE RIETVELD METHOD

Thirty six bentonite samples from 16 different locations were examined in order to demonstrate the applicability of a new Rietveld description approach for quantitative phase analysis. X-ray diffraction patterns of the bulk material were obtained and analyzed by the Rietveld method. The samples contain up to ten different minerals, with dioctahedral smectite as the major component. A model for turbostratic disorder of smectites was formulated inside a structure-description file of the Rietveld program BGMN. The quality of the refinements was checked using an internal standard mineral (10.0 or 20.0 wt.% corundum) and by cross-checking results with X-ray fluorescence (XRF) data. The corundum content was reproduced with only small deviations from the nominal values. A comparison of the chemical composition obtained by XRF and the composition as re-calculated from quantitative Rietveld results shows a satisfactory agreement, although X-ray amorphous components such as volcanic glasses were not considered. As a result of this study, the Rietveld method combined with the new structure model for turbostratic disorder has proven to be a suitable method for routine quantitative analysis of bentonites with smectites as the dominant clay minerals.

Description of X-ray powder pattern of turbostratically disordered layer structures with a Rietveld compatible approach

Abstract We address the problem of the quantitative description of X-ray powder pattern of turbostratically disordered layer compounds. The Debye formula is used, which allows the aperiodic description of any arrangement of atoms. With the extension of Yang and Frindt (1996) for the ideal turbostratic case, these calculations are used to generate reference data that are subsequently treated by the Rietveld method. We are able to show that the case of uncorrelated turbostratic disorder can be modelled equally well in a periodic supercell approach with a single layer in the supercell that is suitable for the Rietveld technique. A brief introduction of this new model was given as an oral contribution at EUROCLAY 2003 (Ufer et al., 2003). The fundamental principles are described in this article because of its complexity. The applicability of this approach to real systems is demonstrated for smectite and corundum mixtures.

Profex: a graphical user interface for the Rietveld refinement program BGMN

Profex is a platform-independent open-source graphical user interface for the Rietveld refinement program BGMN.

Rietveld Refinement Of Disordered Illite-Smectite Mixed-Layer Structures By A Recursive Algorithm. Ii: Powder-Pattern Refinement And Quantitative Phase Analysis

X-ray diffraction (XRD) of powdered materials is one of the most common methods used for structural characterization as well as for the quantification of mineral contents in mixtures. The application of the Rietveld method for that purpose requires structure models for each phase. The recursive calculation of structure factors was applied here to the Rietveld refinement of XRD powder patterns of illite-smectite (I-S) minerals. This approach allowed implementation of stacking disorder in structural models. Models for disordered stacking of cis-vacant and trans-vacant dioctahedral 2:1 layers as well as rotational disorder were combined with models for mixed layering of illitic and smectitic layers.The DIFFaX code was used to simulate non-basal (hk) reflections of illites with different degrees of disorder. Rietveld refinements of these simulated patterns were used to evaluate the application of this new approach. A model describing rotational disorder (n·120° and n·60° rotations) and mixed layering of cis-vacant and trans-vacant dioctahedral layers was tested. Different starting parameters led to identical results within the ranges of standard deviations and confirmed the stability of the automatic refinement procedure. The influence on the refinement result of an incorrect choice of fixed parameters was demonstrated.The hk model was combined with models describing the basal reflections of disordered I-S and tested on measured data. A glauconitic mineral (Urkut, Hungary), an ordered I-S (ISCz-1, a special clay in the Source Clays Repository of The Clay Minerals Society), and a dioctahedral I-S (F4, Füzérradvány, Hungary) were used as test substances. Parameters describing the mixed layering of illitic and smectitic layers were compared with the results from refinements of oriented mounts and showed good agreement. A pattern of a physical mixture of an I-S mineral and a turbostratically disordered smectite was analyzed in order to test the new approach for application in quantitative phase analysis. The quantitative Rietveld phase analysis results were found to be satisfactory.

PREFERRED ORIENTATION OF MINERAL GRAINS IN SAMPLE MOUNTS FOR QUANTITATIVE XRD MEASUREMENTS: HOW RANDOM ARE POWDER SAMPLES?

The degree of preferred orientation of mineral grains in powder X-ray diffraction (XRD) samples prepared by standard techniques has been evaluated by means of a correction model implemented in the Rietveld program, BGMN. It is demonstrated that neither front- nor side-loading of mineral powders obtained by wet grinding in a McCrone micronizing mill yield powder mounts with randomly oriented particles. Despite fine grinding, the primary sizes and shapes of mineral grains contained in multi-phase samples influence the degree of preferred orientation in XRD powder mounts. Two minerals, both of platy habit, were found to show different degrees of preferred orientation in front- and side-loaded samples. In contrast to these methods of sample preparation, the spray-drying technique yielded perfect randomness of the particles. The experiments on artificial mineral mixtures demonstrate that the model applied can effectively correct for preferred orientation allowing reliable Rietveld quantitative phase analysis of moderately textured samples prepared by standard techniques.

RIETVELD REFINEMENT OF DISORDERED ILLITE-SMECTITE MIXED-LAYER STRUCTURES BY A RECURSIVE ALGORITHM. I: ONE-DIMENSIONAL PATTERNS

X-ray diffraction patterns of oriented mounts of clay minerals are often used in clay mineralogy for qualitative and quantitative purposes. Fequently occurring stacking defects, in particular, can be characterized by this technique. Modeling of these diffraction profiles has become an important tool in obtaining structural information about the nature of stacking order. Manual matching of calculated and observed patterns is time consuming and user dependent. Automatic refinement procedures are, therefore, desirable. An improved approach for the treatment of disordered layer structures within a Rietveld refinement is presented here. The recursive calculation of structure factors, similar to that of the simulation program DIFFaX, was introduced in the Rietveld code BGMN. Complete implementation is formulated within the interpreter language of the Rietveld code and is transparent as well as flexible. Such a method has opened the application of Rietveld refinement to patterns of oriented mounts where only basal reflections of stacking disordered structures were recorded. The DIFFaX code was used to simulate basal reflections of illite-smectite mixed layers (I-S) with different ratios of illitic and smectitic layers and with different degrees of long-range ordering (Reichweite). Rietveld refinements with these simulated patterns were used to evaluate the application of this new approach. Several I-S with different degrees of ordering were also chosen as tests for the refinement of basal reflections. The samples were prepared as standard airdried and ethylene glycol-solvated, oriented specimens. Realistic structural parameters were obtained for the composition and ordering of the I-S.

Alternative algorithm for the correction of preferred orientation in Rietveld analysis

Texture effects caused by preferred orientation can be corrected in Rietveld analysis by an alternative algorithm presented in this contribution. This algorithm is equivalent to models using symmetrized linear combinations of spherical harmonic functions, but it is unique to all Laue classes and to all orders. Positive definiteness of the polar-axis density is achieved by the exponential method. The outlined algorithm was tested during Rietveld refinement of selected polycrystal samples. The algorithm was proven to be numerically robust and satisfactorily described deviations from the ideal intensity ratios of the Bragg reflections caused by the texture of the samples.

Termination of swelling capacity of smectites by Cutrien exchange

Abstract The Cu-triethylenetetramine-complex (Cutrien) is one of the commonly used index cations for CEC determination in clay science. Cutrien-exchanged smectites show basal spacings between 13.0 and 13.5 Å after correction for the Lorentz and polarization factors. The full width at half maximum (FWHM) of the d001 reflection is today related to the percentage of tetrahedral charge (beidellitic character) and/or to the Fe content of the smectites. The structural Fe content and the tetrahedral charge correlate, so their individual influence on d001 cannot be resolved. Nevertheless, the FWHM of Cutrien smectites should depend on the charge distribution rather than the Fe content.> X-ray diffraction (XRD) and water uptake capacity measurements showed that the interlayer of Cutrien-exchanged smectites does not swell any more, but can take up a few water molecules. Accordingly, the water uptake capacity of the external surface area can be determined independently from the interlayer water uptake capacity. Adjusting the pH of Cutrien -bentonite dispersion to different values allows for the determination of the variable charge. In conclusion, Cutrien exchange of smectites appears to be suitable for the study of external surfaces area related phenomena (e.g. edge adsorption processes) without any influence of the interlayer region.

LOW-TEMPERATURE HYDROTHERMAL ALTERATION OF SILICIC GLASS AT THE PACMANUS HYDROTHERMAL VENT FIELD, MANUS BASIN: AN XRD, SEM AND AEM-TEM STUDY

Dacitic lava recovered from the immediate subsurface of the submarine PACMANUS hydrothermal vent field exhibits variable degrees of hydrothermal alteration resulting from the interaction of the glassy volcanic rocks with mineralizing hydrothermal fluids at relatively low temperatures. Transmission electron microscopic (TEM) investigations revealed that the felsic volcanic glass transformed to nm-thick smectitic flakes of the montmorillonite-beidellite series via a dissolution and reprecipitation mechanism. The process of smectite formation did not proceed through X-ray amorphous or poorly crystalline transitional phases. Alteration of the glass was found to be most pronounced adjacent to perlitic cracks and vesicles that form an interconnected network focusing fluid flow. Glass dissolution adjacent to these fluid pathways resulted in a characteristic alteration texture at the nm scale; the intensely altered groundmass contains round cavities that are partially coated or filled by smectitic flakes. The Mg content of the smectite broadly increases towards the fluid pathways. Smectitic flakes with compositions corresponding to saponite occur in the intensely altered groundmass adjacent to perlitic cracks. In addition, anatase, apatite and rare kaolinite were formed during the alteration of the volcanic glass. Primary minerals including plagioclase show only minor textural evidence of alteration. However, some primary plagioclase laths show X-ray amorphous rims depleted in Na, Ca and Al. The TEM investigations of the dacitic lava samples from the PACMANUS vent field demonstrate that volcanic glass has a higher susceptibility to hydrothermal alteration at low temperatures than most associated primary phases. The findings of the study suggest that the interaction between the volcanic rock and the hydrothermal fluids proceeded under open-system conditions leading to a mobilization of alkali elements and a redistribution of Ti at the nm scale. The Mg required for the formation of trioctahedral smectite was supplied by the hydrothermal fluids.